Method and apparatus for drying solid articles by heating and cooling



G. LEISCHNER METHOD AND APPARATUS FOR DRYING SOLID ARTICLES BY HEATING AND COOLING March 8, 1949.

Filed Dec. l 8. 1945 Patented Mar. 8, 1949 UNITED STATES PATENT errict t- METHOD AND APPARATUS FOR DRYING SOLID' ARTICLES BY HEATING AND COOLING.

Georg Leischner; Interlaken, Switzerland, assign or Escher Wyss Mascliirienfabriken Aktiemgesell'schatt, Zurich, Switzerland, alcompany Application December 18, 194'5';.Serial' No. 635,622

In Switzerland December 23; 1944 5 Claims. (01. {Mr-13.4)

This invention relatesto a method'fbr' drying solid'goods; for'instan'ce woodi in which" thegoods to be dried are exposed to temperature differences. Methods of this kind have already been described by the inventori'n hispe'nding application Serial'No. 498g335', filed August 12; 1943, now abandoned; According to these methods on the one face of the goods only heating elements and on the other face only cooling elements were provided; while'the expelled moisture flowed off from the heating to the cooling elements.

If these'knownmethod's'are, for instance, used todry timber and these latter arebrought in the form of boards bet-ween a layer of heating" elements and a layer of cooling'el'ements; the boards, on their one face; are heated and, on their other face, cooled. In this way, the distribution of water in the timber ischanged-in that the water is concentrated on the side of the cooling elements. The timberswells up on the side of high humidity, and shrinks on the other; dry side. The timber is thereby warped; and cracks may occur.

This drawback can be obviated if the boards to be dried are turned several times, so that the two outer surfaces of each board are alternately in contact with the heating elements. In this way the direction of difiusion of the water in the timber is'changed several times and a warping of the boards prevented. However, this drying method presents the disadvantage of heat losses, since the cold surfaces of" the boards; on each inversion, must be heated, and the warm surfaces cooled before the diffusion process can again begin. Besides this; the inversion requires additional work and waste of time.

The aimof the" invention' is to overcome these disadvantages and to this end, according to the method of this invention, adjacent parts of the goods to'be dried are'exposed' tothe' influence of heating elements and of at least one cooling element in such a manner that said elements act alternately on adjacent surface sections of the goods t'obedried'.

Another object of theinventio'n is the-provision of an improved apparatus for dryingsolid' goods.

The accompanying drawings illustrate, by way of examples and in a schematic way, diflerent apparatuses for carrying out the method according to the invention" all the apparatuses shown being suitable only for drying pieces of wood.

In the drawing Fig. 1' is an ele'vation (partly in section) of an apparatus for drying wooden boards and Fig. 2 is a horizontal section through this first embodiment of the invention;

Fig. 3 is an elevation (with parts broken away) of a portion or. another example; and

.Fig. 4 is. a horizontal sectionthrough this second' embodiment of the' inventiom Fig; 5- is' a vertical section of an apparatus for drying round timber: and

Fig. 7 is" a cross'section on an" enlarged seal'e through a heating element of theapparatus'sho'wn in Fig. 5, and

Fig; 8 is an upright section of apart of an other apparatus for drying blocks and' round timber;

The drying apparatus shown in Figs; 1 and- 2 designed for drying wooden boards comprises heating elements I and cooling elements 2 which are alternately arranged on either face of the boards 3 to be dried. The heating and cooling elements on' bothfaces of the board's arel placed in reverse order, so that aheating'element on'- the one side lies opposite a cooling? element on the other side. The active surface of 'the coolingielements 2 isloca'ted at a certain distance from the boards 3 so that condensation water-may now: off between the boards-andthe' coolingsurfac'e; The heating elements I", however, make cont-act" with the boards in order to obtain a good heat-transmission. Theheating-elements l mi'ght,however, also be placed at a distance'from the boards 3- to be'treated so that an air gapexists between the latter and the elements I, through which heati's transmitted by radiation. In sucha case" it is advisable to polish the surfaceof 'the heating elements I turned towards the boards 3' in order to augmentreflected radiation. The cooling el'eiments 2,'however, lie always at a distance from the boards. The arrows in Fig. 2 indicate the direction of 'the temperature drops between'heat' ing and cooling elements. These arrows show that the heating elements I and the" cooling ele ments 2 act alternately" on adjacent surface sections of the boards 3 which results in asubstam tially uniform separation of moisture in all directions and in a' flowing off of-the moisture from points of higher temperature towards points of lower temperature;

As illustrated in Fig; 1, the cooling" elements 2 extend towards the bottomso'that: the moisture separated from the boards 3 dropsin: a liquid state'int'o a receiver 4 located below the elements. Aninsulationcasing" 6* prevents heat frombeing exchanged between the apparatus and the surrounding air, while heat-insulatingwalls 1-2' render a direct heat exchange between heating" and cooling elements I" and 2" impossible.

The apparatus shown in Fig: 2" designed" for dryingsimultaneously two rows of boards. It is evident that in lieu of wood board's also" other solid goods of'similarsliapecouldbe dried. The heating. and coolingelements arranged between the two. rows of boards have active surfaces on either: side so that? they act simultaneously" on both rows ofboards: Tlicre arethustfirec group's of elements. The heating and cooling elements located on the same face of the boards 3 form together a battery. The apparatus could also comprise more than three such batteries so as to permit of correspondingly more wood boards being dried simultaneously.

In the embodiment shown in Figs. 3 and 4 the cooling elements 2 have the-shape of plates with bores in which the heating elements I are lodged. These heatin elements project beyond the active surface of the cooling elements 2. They are surrounded by heat-insulating rings 5 preventing direct heat exchange between the elements I and 2. In order to prevent as far as possible heat exchange with the surrounding air, an insulation casing 6 is provided. iHere too, as in Fig. 2, the heating and cooling ielements respectively, lying on the same side of :the goods form a battery, the mutual distance between these batteries being adjustable. The heating elements might have polished active surfaces and be disposed at a distance from the goods to be dried, so that the heat radiates towards the goods. The active surface of the heating elements might also be designed as concave mirror reflectors, e. g. as parabolic mirrors.

' It is advantageous to mount the heating elements I inserted into the rings 5 on springs in order to guarantee a good contact with the boards or other goods to be dried. In Figs. 3 and 4 the heating elements are round; they might, however, have any other shape. In the receiver 4 the condensation water droppin from the cooling surfaces is stored.

Fig. 4 shows a device for drying only one row of boards. As the apparatus shown in Figs. 1 and 2, the one shown in Figs. 3 and 4 may, likewise be equipped with more than two batteries of elements.

In order to increase the heat exchange, the active surface of the elements may be enlarged, for instance, by corrugation or by the provision of ribs.

Owing to the resistance in the air gap between the cooling elements and the goods to be dried, K heat transmission per surface unit from these goods to the cooling elements is smaller than from the heating elements to the goods which are in direct mutual contact. For this reason the heating elements can be smaller than the cooling elements. This allows more heating and cooling elements to be provided on the same surface, and thus, with the same total surface, a

greater quantity of moisture to be eliminated per 'time unit than if the heating elements were of and .8 respectively with the heating elements I and cooling elements 2 respectively, while at the other end of the apparatus similar branch pipes lead to respective outlet collecting conduits. In Fig. 4 a series connection of the heating elements I is indicated in chain-dotted lines H, whilst thedash lines indicate in this Fig. 4 a

series connection of the cooling elements 2. The

same connections might, of course, also be used in Fig. 2 instead of the parallel connection of the heating and cooling elements.

Figs. 5, 6, and 7 show an apparatus in which, for instance, whole, fresh trunks of trees are dried. The heating elements form together a heating body 13 of helicoidal shape surrounding the trunk l2. The active inner surface of this body makes intimate contact with the outer surface of the trunk in order to obtain a good heat transmission. As seen in Fig. '7, the outer surface of the body I3 is provided with a heatinsulating layer l4, so that heat can only be radiated towards the trunk l2. The latter, together with the heating body l3 applied to it, is surrounded by a cooling element constituted by the cylindrical casing I5 of a container. This casing is double-walled. A cooling medium flows through the hollow space I! between the walls IS. The cooling element l5 acts in the intervening spaces defined by the single turns of the heating body l3 (said turns constituting the heating elements) on the trunk l2. In order to avoid heat losses said container is closed at both ends by covers l8. The water issuing from the surface of the trunk i2 is condensed on the cooled casing l5, flows hereupon towards the bottom and is collected in the channel l9 wherefrom itflows oiT through a pipe 20. The arrows in Figs. 5 and 6 show that adjacent parts of the trunk to be dried are exposed to temperature differences of unequal direction, so that the moisture is eliminated uniformly in all directions and deformation of the trunk is prevented.

In Fig. 8 several ring shaped heating elements 2| are provided in lieu of a single heatin element of helicoidal shape. Otherwise the design of the apparatus corresponds to that shown in Fig. 5.

Instead of helicoidal or ring-shaped heating bodies, fiat heating elements of the kind shown in Figs. 3 and 4 could be applied to the surface of the trunk l2. Such heating elements may be designed as reflectors placed at a certain distance from the piece I2 to be dried and radiating heat against the trunk I2.

If, for instance, small heating elements having the shape of plates are used, such elements must be pressed against the outer surface of the trunk l2 by strong springs in order to secure an intimate contact between them and the surface of the trunk. It would, besides, be advantageous to provide the contact surface of these elements with teeth, points or grooves. The heating elements are mounted so as to be adjustable radially to the piece l2, in order that their position may be adapted to the thickness of the body to be dried. All parts of these heating elements which do not enter into contact with the body l2, are insulated in order to avoid heat losses.

What I claim is:

1. Drying apparatus particularly for wooden boards, comprising in combination at least two rows of heating and cooling elements, said heating and cooling elements being arranged in the longitudinal direction of each of said rows alternately side by side, a heating element of one of said rows being arranged opposite a cooling element of the other row, and vice versa, each two rows defining an intervening space adapted to the size of the goods to be dried and intended to be inserted between two rows, and means for supporting the boards between the rows in spaced relation from the cooling elements. I

2. Drying apparatus particularly forfwooden boards, comprising in combination at least two rows of heating and cooling elements, said heating and cooling elements being arranged in the longitudinal direction of each of said rows alternately side by side, a heating element of one of said rows being arranged opposite a cooling element of the other row, and vice versa, the active surfaces of said cooling elements bein set back with regard to the active surfaces of said heating elements, and said two rows defining an intervening space adapted to the size of the goods to be dried and intended to be inserted between two rows, and means for supporting the boards between the rows in spaced relation from the cooling elements.

3. In a method for drying solid members, such as Wooden boards, consisting in exposing the members to be dried throughout their entire length to the influence of at least two opposed rows of heating and cooling elements by inserting said members between such rows, said heating and cooling elements arranged in the longitudinal direction of the rows having all substantially the same length, and a heating element of one of said rows being arranged opposite a cooling element of the other row, and vice versa; and bringing said heating elements into contact with the members to be dried, while the latter remain spaced from the cooling elements.

4. Drying apparatus, particularly for drying wooden boards, comprising in combination at least two opposed rows of heating and cooling elements all having substantially the same length and defining an intervening space adapted for the size of the boards to be dried and intended to be inserted between two such rows, said heating and cooling elements being arranged in the longitudinal direction of each of said rows alternately side by side, and a heating element of one of said rows being arranged opposite a cooling element of the other row, and vice versa; and an insulating casing enclosing all of the said heating and cooling elements and having transverse partitions, the end walls of said casing and its partitions being provided with openings adapted to the size of the boards to be inserted between two of said rows, the inserted boards being maintained in the required position by said end walls and transverse partitions, and the active surfaces of said cooling elements being set back relative to the active surfaces of said heating elements, so that the cooling elements are spaced from the boards inserted between two rows of heating and cooling elements.

5. Drying apparatus according to claim 4, in which means are provided for interconnecting adjacent heating and cooling elements of each row to a battery.

GEORG LEISCHNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 286,552 Noyes Get. 9, 1883 688,152 Atwood Dec. 3, 1901 1,045,623 Smith Nov. 26, 1912 1,413,786 Robertson Apr. 25, 1922 1,613,073 Zimmerli Jan, 4, 1927 1,842,195 Pinder Jan. 19, 1932 2,065,636 Whipple et a1 Dec. 29, 1936 2,320,474 Ross June 1, 1943 2,370,811 Osgood, Jr. Mar. 6, 1945 FOREIGN PATENTS Number Country Date 437,665 Germany May 15, 1925 

